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([240e:370:8b13:97f0:154c:a6ff:49c9:f239]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-72f8a6b3f86sm9708981b3a.67.2025.01.28.07.59.10 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 28 Jan 2025 07:59:16 -0800 (PST) Message-ID: Date: Tue, 28 Jan 2025 23:59:07 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [linus:master] [x86] 4817f70c25: stress-ng.mmapaddr.ops_per_sec 63.0% regression Content-Language: en-US To: David Hildenbrand , Peter Zijlstra Cc: kernel test robot , oe-lkp@lists.linux.dev, lkp@intel.com, linux-kernel@vger.kernel.org, Andrew Morton , Dave Hansen , Andy Lutomirski , Catalin Marinas , David Rientjes , Hugh Dickins , Jann Horn , Lorenzo Stoakes , Matthew Wilcox , Mel Gorman , Muchun Song , Peter Xu , Will Deacon , Zach O'Keefe , Dan Carpenter , Rik van Riel References: <202501281734.d408a35b-lkp@intel.com> <46ea4509-0f38-4b22-bd91-f05c68db2562@redhat.com> <20250128113100.GB7145@noisy.programming.kicks-ass.net> <2c599f1f-f63b-4504-a026-46bf73954124@redhat.com> <20250128132847.GB505@noisy.programming.kicks-ass.net> <18172465-37e3-48a9-9d67-0d44fdcb93bd@redhat.com> From: Qi Zheng In-Reply-To: <18172465-37e3-48a9-9d67-0d44fdcb93bd@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 2025/1/28 21:42, David Hildenbrand wrote: > On 28.01.25 14:28, Peter Zijlstra wrote: >> On Tue, Jan 28, 2025 at 12:39:51PM +0100, David Hildenbrand wrote: >>> On 28.01.25 12:31, Peter Zijlstra wrote: >> >>>>> I recall a recent series to select MMU_GATHER_RCU_TABLE_FREE on x86 >>>>> unconditionally (@Peter, @Rik). >>>> >>>> Those changes should not have made it to Linus yet. >>>> >>>> /me updates git and checks... >>>> >>>> nope, nothing changed there ... yet >>> >>> Sorry, I wasn't quite clear. CONFIG_PT_RECLAIM made it upstream, >>> which has >>> "select MMU_GATHER_RCU_TABLE_FREE" in kconfig. >>> >>> So I'm wondering if the degradation we see in this report is due to >>> MMU_GATHER_RCU_TABLE_FREE being selected by CONFIG_PT_RECLAIM, and >>> we'd get >>> the same result (degradation) when unconditionally enabling >>> MMU_GATHER_RCU_TABLE_FREE. >> >> Ah, yes, put a RHEL based config (as is the case here) should already >> have it selected due to PARAVIRT. > > Ah, right. Most distros will just have it enabled either way. > > But that would then mean that MMU_GATHER_RCU_TABLE_FREE is not the cause In addition, commit 718b13861d22 ("x86: mm: free page table pages by RCU instead of semi RCU") also made a change, that is, when freeing a single page table pages, use RCU to free the page table page instead of sending the IPI. But in theory this should not cause performance regression, and I have tested the performance of munmap with bpftrace and found no regression. > for the regression here, and something else is going wrong. It looks like it, I will investigate it carefully. Thanks! >